Black-footed Ferret Recovery

Black-footed ferrets, an endangered species, were first reintroduced in Montana in 1994 on black-tailed prairie dog colonies located at UL Bend National Wildlife Refuge. Black-footed ferrets require at least a few thousand acres of healthy prairie dog colonies to provide habitat and prey because they are obligate predators of prairie dogs and they live in the tunnel systems created and maintained by prairie dogs. Many public land managers and landowners have a general intolerance for very many acres of prairie dogs and throughout the black-footed ferret’s historical range, generally small and fragmented prairie dog colonies are limiting ferret recovery. In addition to limited human tolerance of prairie dogs, outbreaks of sylvatic plague can eliminate thousands of acres of prairie dogs in a few weeks, thus eliminating expansive areas of black-footed ferret habitat. In addition, ferrets exposed to plague die within 3 days. Plague was first detected in Phillips County, Montana in 1992 when many prairie dog colonies suddenly disappeared. By 1996, nearly 80 percent of 26,000 acres of prairie dog colonies had died out.

Sylvatic plague is a nonnative disease foreign to the evolutionary history of North American species. Plague was inadvertently introduced into the United States around 1900. Sylvatic plague is a bacterial infection transmitted primarily by infected fleas. It can affect the black-footed ferret directly via infection and subsequent mortality or indirectly through the disease’s effects on prairie dogs and the potential for dramatic declines in the ferret’s primary prey. Plague can be present in a prairie dog colony in either an enzootic state (persistent, low level of mortality) or epizootic state (high mortality). Recovery efforts for the ferrets are hampered because both ferrets and prairie dogs are extremely susceptible to plague.

Despite these obstacles, a huge amount of effort has gone into trying to establish black-footed ferrets in north-central Montana. There have been 229 captive-reared ferret kits released in three areas of the UL Bend Refuge, 95 north of the refuge on BLM lands and 167 in two areas of the Fort Belknap Indian Reservation. In addition, at least 236 wild-born kits have been observed at the UL Bend Refuge.

During 2007 and 2008, epizootic plague eliminated about 60 percent of the prairie dog acreage where ferrets had resided at the UL Bend Refuge. Plague was also reported to be widespread north of the refuge and was eliminating a substantial portion of remaining prairie dogs throughout Phillips County. To protect the remaining prairie dogs and resident ferrets, all remaining active portions of prairie dogs towns were treated with insecticide during early summer 2008 to kill fleas. More than 34,000 burrows were treated, and all colonies continue to appear active and healthy.

Despite the failure to establish a self-sustaining black-footed ferret population in Montana, the Service remains hopeful that a ferret population contributing to the rangewide recovery of the species will be established in Montana. Already, much has been learned along the way that has greatly helped national efforts for ferret recovery. For example, Matchett et al. (2010) has shown that in addition to epizootic plague affecting ferrets, enzootic plague (that is, the presence of disease-causing Yersinia pestis when there is no noticeable decrease in prairie dog abundance) also reduces ferret survival and that both flea control and an experimental plague vaccine for ferrets were effective. It is likely that if an oral plague vaccine can be developed, prairie dog numbers will increase and stabilize on the refuge, and the area may be able to sustain a population of ferrets that will contribute to its recovery rangewide. To learn more about black-footed ferret recovery nationwide, visit the National Black-footed Ferret Conservation Center website.